The present invention relates to a unique polymeric material composed of polyamides and polyalkylene constituents and methods for making the same. More particularly, the present invention pertains to polymeric materials which contain polyamides and polyalkylenes in an alloyed relationship which permits orientation of polyamide and polyalkylene functionalities resultant to molding processes. Even more particularly, this invention pertains to alloys made up of polypropylene and polyamide constituents heretofore considered to have less than optimal compatibility.
The need and demand for molded polymeric component parts is significant. Such component parts provide functional versatile, low-cost, lightweight solutions for many elements in a myriad of products from automotive vehicles to construction components to decorative objects. Various molding techniques exist to process various thermoplastic and thermosetting materials into finished components. The choice of polymeric material is generally governed by factors which include the type of molding process to be employed and the physical characteristics which the finished component must possess. Such characteristics can include, but are not limited to, strength, flexibility, weatherability and resistance to degradation upon prolonged exposure to harmful elements such as UV light, ozone etc. Desirable material characteristics can also include the ability to withstand repeated fluctuations in temperature as well as upper and lower service limits compatible for the use to which the components are to be put. Additionally, there is a great demand for moldable polymeric compounds and formulations which will provide desirable characteristics such as scratch resistance, abrasion resistence, and optimum paintablity normally attributed to the xe2x80x9charderxe2x80x9d melt processible thermoplastic polymeric materials together with overall flexibility typically found in xe2x80x9csofterxe2x80x9d polymeric compounds.
All too often, the compromise between desired physical characteristics is one which cannot be satisfactorily achieved or can only be attained in a cost intensive and or labor intensive manner. For instance, in situations where external surface scratch resistance and all-body flexibility and/or general strength is required, it has generally been thought that multi-layer laminates of various polymeric materials may be the solution. Other solutions include the use of various paints, lacquers or other surface tougheners applied in bonded relationship to the softer substrate in order to provide characteristics such as enhanced scratch resistance and the like. This is problematic as such applied coatings and/or bonded laminates require careful surface preparation and are susceptible to scratching or peeling over the life of the part or component.
Compositions have been proposed which include two or more different polymeric compositions in order to obtain desirable combinations such as scratch and mar resistance, paintability, etc. Unfortunately, multi polymer compositions often exhibit undesirable flow characteristics during melt processing and yield finished parts with undesirable performance characteristics. These undesirable surface performance characteristics include, but are not limited to, delamination of some or all of the surface layer of the part produced.
There are also situations in which it is desirable to prepare polymeric parts which are colored or pigmented. This can be problematic in situations where multipolymer compositions are employed. In many situations, polymeric parts or components made through injection molding processes exhibit uneven pigmentation. This phenomenon can be due to uneven or inappropriate polymer flow characteristics during part formation. In other situations, it is desirable to provide a polymer which can incorporate specialty aesthetic additives such as metal flake in a pigmented or non-pigmented substrate in a manner which is aesthetically homogeneous and which does not materially impair or compromise key functional characteristics of the material such as strength and durability.
In order to process dissimilar polymers to form polymeric compounds suitable for use in molding processes such as injection molding, it has heretofore been considered necessary to employ significant quantities of compatibilizing agents such as maleic anhydride functionalizing agents to functionalize the polymeric components and facilitate bonding. These materials have been considered mandatory to permit the two or more dissimilar polymeric materials to blend effectively in initial formulation steps and to process effectively in the subsequent part formation steps such as injection molding processes.
Historically, it was considered common knowledge that omission of such functionalizing agents would result in the failure of the two or more materials to melt process in a compatible manner. It was believed that functionalizing agents such as maleic anhydride permitted polymeric materials having vastly different properties such as melt temperature and the like to blend, melt and reform effectively upon subsequent heating and processing. Such functionalizing agents are typically so effective that an essentially uniform polymeric blend results. This compromises any potential for ordered orientation of individual polymer components in subsequent molding or polymer forming operations.
Thus, it would be desirable to provide a melt processible polymeric composition which is composed of two or more polymeric components which, when subjected to molding operations such as injection molding or extrusion, provides a finished product or part which exhibits at least one of the following characteristics:
a) scratch and mar resistance in the surface of the finished product produced from the material;
b) surface characteristics of the finished part which contribute to direct paint ability, i.e. adhesion of paint and/or other applied materials to the surface of the produced part without requiring the use of an adhesion promoter and/or a tie coat
c) mold in color capability, i.e. the ability to integrate coloring agents such as pigments into the material at a point prior to molding or melt processing into the finished part;
d) enhanced exterior weatherability;
e) enhanced or elevated resistance to heat and/or other environmental hazards.
It is also desirable that the melt processible polymeric material thus formed be one which retains key characteristics of the individual component materials upon processing and mold formation. It is also desirable to provide a melt processible polymeric material which can contain at least two essentially non-compatible polymeric materials in orientable alloyed relationship to each other. Finally it is desirable to provide a polymeric composition which permit or promotes migration of one polymer relative to another during the molding or other melt processing operations such as extrusion.
The present invention is directed to a polymeric composition which is suitable for use in injection molding processes and procedures. The polymeric composition contains, as a major portion, an olefinic polymer component selected from at least one a group which includes polyalkylenes, copolymers of polyalkylenes, in which at least one monomeric unit of the polymer contains between 2 and 6 carbon atoms. The polymeric composition of the present invention contains, as a minor portion, a thermoplastic polyamide, with polyamides such as polyamide 6, polyamide 6,6, polyamide 11 and polyamide 12 being preferred. The polyamide and olefinic polymeric components are present in random orientable locations in the initial polymeric composition.
The polymeric composition of the present invention possesses unique orientation characteristics when injection molded against a temperature gradient such that the resulting workpiece has distinctive regions of elevated polyamide concentration proximate the outwardly oriented surface and distinctive regions of elevated olefinic polymeric concentration proximate to interior regions of the workpiece.